Mercury switch



Patented May 9, 1950 UNITED STATES PATENT OFFICE Application October 19, 1945, Serial No. 623,279 In GreatBritain October 1-7, 1944 Section 1, Public-Law 690, August s, 1946 Patent expires October 17, 1964 4 Claims. 1

I This invention relates to mercury switches. The object of the invention is the provision of an improved mercury switch whose moving parts are entirely sealed, so that it can for example, be employed for an indefinite period under water, and which moreover can be used for very long periods without deteriorating or requiring attention.

The invention consists broadly of an electric switch of the mercury type, comprising a sealed envelope, a main body of mercury contained. in said envelope, a movable device located in said envelope, said movable device comprising insulating material and magnetic material, and having formed in the insulating material a cup. or recess which contains mercury, means outside said container for magnetically controlling said movable device through the magneticmaterial thereof, in such a way that said movable device can be alternatively positioned with the mercury in the cup or recess in union with, or out of contact with, the main body of mercury, a conductor passing in sealed relation in said envelope so that it dips in the mercury in the cup or recess throughout the movement ofsaid device, and another conductor in electrical connection with said main body of mercury, so that electrical connection is established or disestablished between the two conductors, according to whether the mercury in the cup is in union with, or out of contact with, the main body of mercury.

In order that the invention may be the more clearly understood, examples of mercury switches in accordance therewith will now be described, reference being made to the accompanying drawings, wherein Figure 1 is a sectional elevation of a switch in accordance with the invention at the open position;

Figure 2 is a similar view of the same at the closed position;

Figure 3 is a similar view of an alternative form of a part of the preceding Figures.

Figure 4 is a similar view of another switch in accordance with the invention at the open position;

' Figure 5 is a section on line V-V of Figure 4;

Figure 6 is a sectional elevation of an alternative form of a part'of Figure 4;

' Figure '7 is a section on line VII-VII or Figure 6;

Referring first to Figure l the switch comprises a fiied outer envelope l of glass which is of roughly cylindrical form and is disposed with its axis vertical. This envelope has a quantity of mercury 2a in it, and, floating in this mercury; is

an upright cylindrical body 3 of refractory mate rial formed at its upper end with a deep cupped recess 4 which is completely filled with a further quantity of mercury 2b. A vertical upper conductor 5 is sealed in the upper end of the envelope l and eXtends axially downwards into the incr cury 2b in the said cupped recess 4, and a lower conductor 5 is sealed in the lower end of the en velope and has its inner end immersed in the mercury 2a in the envelope.

Normally the refractory body 3 fioatsas m Figure 1 with its upper end well above the level of the mercury 2a in the envelope, andtherefore the two quantities of mercury 2a and 2b are out of contact, and no contact is established between the two conductors 5 and 6. The refractory body 3 has a cylindrical piece of iron 1 or other magnetic material attached coaXially to it at its lower end so as to form a continuation of it, and means are provided such as a solenoid 8, outside the envelope I for setting up a magnetic field which will pull said piece of iron I, and therefore the refractory body 3, downwards until said refractory body is under the surface of the mercury in the envelope as shown in Figure 2. It will be seen that, as the top of said refractory body 3 passes just beneath the level of the mercury 2a in the envelope, the two quantities of mercury 2a and 2b will joinone another to form a single body 2, and electrical connection between the two conductors 5 and 5 will accordingly be established. When the magnetic field is cut oii the refractory body 3 will again rise and contact will be again broken. It will of course be understood that the cupped recess t in the top of the refractory body 315 sufficiently deep, and the upper conductor 5 projects sufiiciently far into it, to ensure that said upper conductor never breaks contact with the mercury 21) in said cupped recess.

It will be seen that contact is always made and broken between mercury and mercury, and never between mercury and a solid conductor. Also the region at which contact is made and broken is always immediately above the annular topsurface 9 of the refractory body surrounding the cupped recess, and the refractory material of said body is of a nature not to be damaged by the making and breaking of contact. This annular top is convexlyrounded as shown so that the mercury flows easily over it to make and break contact.

To protect the glass envelope the inside surface thereof is lined with refractory material l0 extending at least over theregi'on opposite to where contact is made and broken.

Any suitable refractory material may b'e'em ployed for the refractory body 3 and the refractory lining In, for example alumina, magnesia berillia, thoria. At the moment the preferred material is alumina.

In construction it will be seen that the mag netic extension I is made tubular so as to D vide a bore into which the lower conductor 3 projects. The lower part of the envelope I, which is surrounded by the solenoid 8, is of reduced diameter as shown. Even when the floating unit is at its upper position the magnetic extension I just projects into this reduced diameter portion into which it fits fairly closely, and thus the centering of said unit is ensured. At the same time considerable clearance is provided around the upper portion at which the make-and-break takes place.

Referring now to Figure 3, this illustrates an alternative in which the magnetic element 1a of the floating unit is completely embedded and hermetically sealed in the cylinder 3a of refractory material. In this arrangement the cylinder 3a is extended further downwardly than the equivalent cylinder 3 of Figures 1 and 2, and is formed with a coaxial bore hole H in its lower end, in which the conductor 6 extends. The magnetic element 1a is formed as a tube and is completely embedded in the annular wall surrounding the bore hole I I. This is done by boring an annular reces in the lower end of the said annular wall, of dimensions to just receive the tubular magnetic element la, and, when the latter is inserted, covering the open end of said recess with a suitable cement.

In all other respects the arrangement will be the same as that of Figures 1 and 2.

Referring now to Figures 4 and 5, these show a somewhat modified construction in which the envelope I2 is of magnetic steel. In this case, the vertical upper conductor I3 is sealed in the upper end In of theenvelope I 2 in such a way that it is insulated from the steel. The other conductor does not need to be sealed in the lower end of the envelope l2 but is simply connected to the outside of said envelope.

For sealing the upper vertical conductor l3 in the upper end of the envelope l2 a bush M of porcelain is sealed in an opening in the top l2a of said envelope, and the conductor is passed through, and sealed in, this bush. For sealing this bush I4 both to the steel of the envelope and to the copper of the conductor, the appropriate parts of said bush may be coated with silver and solder l5 may be added to elfect the seals.

The lower end 13a of the conductor is which actually dips into the mercury is made of tungsten, and the copper portion l3b of the conductor and also the silver for eifecting the aforesaid seals is protected from mercury vapour by means of a pad it of refractory cement, such as talcum powder and a silicate binder covering the underside of the top portion I2a of the envelope .l and also the bottom of the bush l4, and sealed round the conductor I3. In construction, the conductor l3, the bush I4 and the pad iii are united to form a unit with the top portion l2a of the container, and this top portion is then welded to the main portion. The level of the pad I6 is below the upper end of the tungsten portion l3a of said conductor.

To ensure good electrical connection between the envelope l2 and the other conductonsaid envelope is coated with copper I! and the conductor is connected to this copper coating, say by clipping or clamping.

The arrangement of Figure 4 is also modified in that means are provided whereby restricted and confined arcing mercury path is provided in parallel with the main make-and-break path, at which arcing path the circuit is actually broken. Being restricted and confined, the mercury formin this arcing path will vaporise at the moment the circuit is broken, and the high pressure of mercury vapour thus formed will rapidly extinguish any arc.

To this end, one or more fine arcing holes l8 are formed from the outer periphery of the refractory body 3 into the cupped recess 4 in the upper end of said refractory body, said holes extending at an angle upwardly.

When the floating body is at the up, or circuitbreaking, position, the said arcing holes 18 will be above the level of the outside mercury 2a and will be at least partially empty. When the floating body is drawn down to the contact-making position, its speed of movement is such that contact will be made as before described, above the annular top surface 9 of the refractory material, before the mercury has time to fill the fine arcing holes i8, which it subsequently does. When said floating body again floats up to its circuit-breaking position, the circuit will be maintained through the mercury in said arcing holes I8, after the mercury has separated above the annular top 9 of the refractory material. Considerable heat will be generated in the mercury in said arcing holes I8, and said mercury will boil, thereby effecting a breach in its continuity within the arcing hole, and breaking the circuit. The high pressure at the breach will rapidly extinguish any arc which may be formed.

Referring to Figure 6, this shows a further modification according to which vents IQ of capillary magnitude are provided extending upwardly from the holes 58 at about the mid points of the latter. Where these vents 59 break out at the top 9 of the refractory body, the refractory material is built up around the vents so as to form narrow chimneys 20 extending upwardly from the upper end of the refractory body. These chimneys 26 extend up sufficiently far to ensure that the upper ends of the vents are always out of the mercury. The purpose of the vents I9 is to permit of the escape of entrapped gas, which might in some cases, prevent the joining of the mercury inside the arcing channel l8 during subsequent operation.

It will be seen that in Figure 6 the arcing holes 18 are shown horizontal.

In all the embodiments, the floating unit flts fairly closely in the lower end of the envelope as described with reference to Figure 1. Thus as the solenoid 8 fits fairly closely around the said lower end of the envelope the best magnetic efficiency is obtained. This necessitates the provision of means for permitting the mercury to pass freely to and from the more or less trapped space at the bottom of the container when the floating unit rises and falls.

In Figure l, the means consist of one or more openings 24 formed in the upper edge of the tubular piece of iron '5. In Figure 3 they take the form of a number of passages 2| extending from the top of the bore hole I l to the outside of the refractory cylinder 3a. In Figures 4 and 5, they take the form of radial grooves 22 in the upper end of the tubular piece of iron 1, and in Figures 6 and 7 they are shown as taking the form of longitudinal grooves 23 in the outer periphery of the iron piece 7, which in this case is not necessarily tubular.

In practice it may be suitable in all the embodiments to limit the upward movement of the floating unit by the abutting of the lower end of the conductor i3 against the bottom of the cup or recess M.

It is usually desirable to evacuate the envelope, or it may be filled with an inert gas.

What I claim and desire to secure by Letters Patent is:

1. An electric switch of the mercury type, comprising a sealed envelope containing a main body of mercury, a member of insulating material at one end portion and magnetic material at the opposite portion having a recess in the insulated end portion opening to said end and containing a secondary body of mercury and a series of holes of small diameter in the wall of the insulated end portion communicating with the recess, said member normally floating in the main body of mercury with the holes positioned above the main body of mercury and the secondary body of mercury out of contact with the main body of mercury, a pair of electric conductors, one of said electric conductors being in permanent connection with the main body of mercury and the other conductor being in constant connection with the secondary body of mercury, and means to attract the magnetic end portion of the member and move said member into the main body of mercury to position the opening to the recess below the surface of the main body of mercury, the movement of the member into the main body of mercury causing the main body of mercury to contact the secondary body of mercury through the opening to the recess before the series of holes are filled with the mercury, and said series of holes preventing arcing during the movement of the member to its floating position.

2. An electric switch as claimed in claim 1, wherein the series of holes incline from the exterior of the member to the recess.

3. An electric switch of the mercury type, comprising a sealed envelope containing a main body of mercury, a member of insulating material at one end portion and magnetic material at the opposite end portion having a recess in the insulated end portion opening to said end and containing a secondary body of mercury and said member provided with a passage in the wall of the insulated end portion communicating with the recess and a vent hole extending longitudinally of and in the wall of the member with one end communicating with the passage and the op posite end opening through the end of the insulated end portion of the member, said member normally floating in the main body of mercury with the secondary body of mercury out of contact with the main body of mercury, a pair of electric conductors, one of said electric conductors being in permanent connection with the main body of mercury and the other conductor being in constant connection with the secondary body of mercury, and means to attract the magnetic end portion of the member and move said member into the main body of mercury to position the opening to the recess below the surface of the main body of mercury, the movement of the member into the main body of mercury causing the main body of mercury to contact the secondary body of mercury through the opening to the recess before the passage is filled with mercury, and said passage preventing arcing during the movement of the member to its floating position.

4. An electric switch as claimed in claim 3, wherein the end of the insulated end portion of the member is provided with a chimney extending from said end, and the vent hole extends through said chimney.

EGON BENEDIKT BABLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,010,620 Crumpton Dec. 5, 1911 1,228,058 Schmidt May 29, 1917 1,786,018 McCabe Dec. 30, 1930 1,861,630 Hatay June 7, 1932 1,930,094 Hatay Oct. 10, 1933 2,003,260 Green May 28, 1935 2,232,874 Larson Feb. 25, 1941 12,396,956 Larson Mar. 19, 1946 FOREIGN PATENTS Number Country Date 111,171 Germany June 20, 1900 443,289 Germany Apr. 26, 1927 473,603 Great Britain Oct. 15, 1937 

